Acid‐Promoted Divergent and Chemoselective Annulation of 2‐(Methylthio)‐2‐Thioxoacetates for the Synthesis of 4‐Oxo‐3,4‐Dihydroquinazolines and 4‐Oxo‐4H‐Benzo[d][1,3]thiazines

A divergent and chemoselective method to quinazolinones and benzothiazinones has been developed through the reaction of alkyl/arylmethyl 2‐(methylthio)‐2‐thioxoacetate with 2‐aminobenzamides under Brønsted acid catalysis. The reaction delivered two structurally distinct heterocyclic scaffolds under different reaction conditions from a common synthetic precursor. The use of p ‐toluenesulfonic acid ( p ‐TSA) in DMF afforded quinazolinone derivatives in good yields, while reactions performed in an AcOH/DMF (1:1) medium produced the corresponding benzothiazinones with excellent chemoselectivity. The methods demonstarte broad applicability under transition metal‐free conditions. The structures and chemoselective cyclization of representative products were unequivocally furnished by spectroscopic characterization and single‐crystal X‐ray diffraction analysis.